1. Field of the Invention
The present invention relates to a herapathite which is utilized in a light controlling device such as an optical valve or the like, and to a process for producing the same.
2. Description of the Related Art
A clathrate compound which includes quinine and iodine and which is shown in FIG. 15 is called a herapathite. The herapathite has been known that it is useful in optical applications because of its polarizability of light. In the crystal of the herapathite, the iodine atoms are oriented as illustrated in FIG. 15. Hence, there arises a dipole in the orientation direction.
When the herapathite is made into capillary crystals, it is possible to construct a particles dispersion type display device. Namely, the capillary herapathite crystals are floated in an appropriate organic dispersion medium, and the thus obtained suspension is filled into a panel which has electrodes therein. When an electric field of a predetermined direction is applied to the panel, the herapathite crystals which have been floating in the organic dispersion medium are aligned in a predetermined direction because of their dipoles. When the application of the electric field is stopped, the herapathite crystals are disoriented and are mixed each other at random in the organic dispersion medium. Hence, the herapathite can be employed in a light controlling device such as an optical valve or the like by utilizing its characteristics above mentioned.
As for a process for producing the capillary herapathite crystals, there is a process which is disclosed in Japanese Examined Patent Publication (KOKOKU) No. 20560/1973. As set forth in the publication, quinine or preferably quinine sulfate is dissolved into the aqueous solution of sulfuric acid and acetic acid in the presence of iron ions. Then, iodine and potassium iodide are added to the resulting solution to produced a clathrate compound. Thereafter, the thus precipitated crystals are filtered and dried to get the capillary herapathite crystals. The herapathite crystals obtained by this process have iodine atoms which are oriented in parallel with the minor axis of the crystals. This orientation of the iodine atoms result in a problem such as a slow responding speed when the herapathite crystals are applied to the light controlling device or the like.
Further, the herapathite crystals obtained by this process have the problems of the heat deterioration.
For example, one may think of employing the above-mentioned herapathite crystals for an automobile windshield glass so that a driver can control the light transmittance of the windshield glass. For this purpose, it is necessary to fill the herapathite crystals into the laminated glass in the process of producing an automobile windshield glass. However, it has been known that the herapathite crystals obtained by the above-described conventional production process are decomposed or degraded at a temperature of 110.degree. C. or more. Therefore, the herapathite crystals cannot be filled into the laminated glass which is processed to the automobile windshield glass at a high temperature of 130.degree. C. or more.